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Guglielmo Tino's group

Ultracold atoms and precision measurements

Ultracold atoms and precision measurements

Optical atomic clock


The recent availability of optical frequency-combs has made possible, for the first time, direct optical frequency measurements. This, in turn, opened the way to atomic clocks based on optical transitions which could be superior in accuracy and in stability compared with the actual microwave atomic standards. Among all possible atomic sources, a sample of neutral Sr atoms has been considered as one of the most interesting candidates because of the simple level scheme which presents a set of transitions well suited for laser cooling down to almost quantum degeneracy, as well as narrow linewidth clock-transitions (linewidth <1mHz for the fermionic 87Sr isotope). We intend to define a new frequency standard, referenced on visible transitions of atomic strontium.


Ultra-cold Strontium experiment and short distance measurements

We are currently developing and studying new interferometric schemes based on ultra-cold strontium atoms. The aim of the project is high precision measurements of gravity acceleration for fundamental tests of General Relativity.
In the past years our work has focused on cooling, trapping and manipulating ultra-cold 88Sr, most abundant bosonic isotope of strontium. This isotope is well suited for precision measurements because of its particular properties. Amongst the known elements, 88Sr possesses the unique characteristic of an almost vanishing scattering length. This means that a cold ensemble of 88Sr can be considered as an ideal system of non-interacting particles. The most important consequence is the absence of decoherence among the external degrees of freedom due to the absence of cold collisions. Thanks to this property, long-lived Bloch oscillations in a vertical optical lattice could be observed up to 20 s with transfer of more than 1000 photon recoils.
Furthermore, 88Sr has a zero nuclear moment, and because of the presence of two valence electrons, the energetic ground state does not present any electronic moment. Therefore, 88Sr has a zero total magnetic moment in its ground state, making the isotope insensitive to external magnetic fields. This is a precious characteristic for implementation in high precision measurements experiments, where the control of the spurious magnetic field is a real technical issue.
Another interesting feature of strontium isotopes is the presence of narrow optical transitions. Such resonances can be used to produce ultra-cold thermal samples down to the recoil limit, and allow the implementation of fast optical cooling schemes toward quantum degeneracy. Ultra-narrow optical transitions also allow the development of the most stable and accurate optical clocks.
We have acquired a wide knowledge in the coherent control of the quantum motion of atoms in optical lattices by means of resonant tunnelling techniques. This system demonstrated superior performances in precise measurements of forces at the um scale, and it is of great interest in short distance measurements.
We have also used this system to perform differential gravity measurements between the 88Sr and the 87Sr isotopes to test Einstein Equivalence Principle (EEP). The employment of this combination of test probes is of special interest, as they not only have different masses but also possess a deeply different quantum structure. They undergo different statistics (one is a boson and one is fermion), and furthermore the bosonic isotope is completely spinless. With this system we were able to test the EEP at 10-7 level and put a constraint on the spin-gravity coupling violation.
In order to drastically improve the performances of the gravimetric measurements, we are currently developing a new interferometric scheme based on Large-Momentum-transfer Bragg pulses and Bloch oscillations. With the powerful coherence properties of 88Sr, the highest performances of this kind of interferometers are foreseen.

Useful resources
  • More info about Strontium atom and his interest in ultra-cold atom physics



Magia and gravity measurement

Atom interferometry gravity-gradiometer for the determination of the Newtonian gravitational constant G

The goal of MAGIA experiment is the high precision measurement of the Newtonian Gravitational Constant G using atom interferometry.

More than 300 measurements have been done, but there are only a few methods which can be considered conceptually different: torsion balance, torsion pendulum, beam balance and pendulum cavity.

All these methods have in common that masses, which probe the acceleration caused by well known source masses, are suspended, for instance with fibers. This possible source of systematic effects can be eliminated if one performs a free-falling experiment.

Free falling Rb atoms will be used as probe masses to test the gravitational acceleration of nearby source masses. The combination of Raman atom interferometry and laser cooling will allow us to achieve high sensitivity. Using atoms with well known properties, instead of macroscopic probe masses, will help to reduce systematic errors and permit an accuracy at the level of 10-4.


Transportable gravimeter

Coherent matter-wave optics is still a very young field, far less developed and more complex than conventional optics for light. This field represents an emerging area of science, quantum engineering, with a high potential for a future technology and multidisciplinary applications.

Thanks to an impressive evolution and remarkable inventions, the ultimate potential of matter-wave sensors is entirely open. For the closely related field of atomic clocks, the growth in performance was exponential during the last decades! This is the reason why matter-wave sensors are considered as one of the most promising fields to progress in metrology and fundamental tests. On the other hand, it is still an open question, if quantum engineering will once become a technology with major applications (beyond clocks) in every day life. Inertial quantum sensors provide a new tool for the precise detection of faint forces and tiny rotations. According to the principle of these sensors, the measured physical quantity will be converted into a frequency, which can be measured with highest accuracy (nowadays, time and frequency standards are the most precise standards).

The outstanding feature of these sensors is the precisely known scaling factor: there is no need for calibration, which predestines these sensors for inertial references and for applications for the Système International.